#include <fstream>
using namespace std;

int main()
{  
	bool ok[2000000];
	int nr = 0;
	ifstream fin("ciur.in");
	int i, j, n;
	fin >> n;
	fin.close();
	for ( i = 2; i <=n ; i++)
		ok[i] = true;
	for ( i = 2; i <= n; i++)
		if ( ok[i] )
		{
			nr ++;
			for ( j = i; j <= n; j += i )
				ok[j] = false;
		}
	ofstream fout("ciur.out");
	fout << nr << '\n';
	fout.close();
	return 0;
}